Transparent displays are long sought-after by scientists and engineers. Two-dimensional (2D) transparent displays can create images that appear to float in the air, in contrast to traditional displays where images appear on a visible screen. Aside from creating special visual impressions, such displays can have a wide variety of applications. A glass window can be turned into the screen of a home theater. Eyeglasses can become a mini computer screen. The windshield of a vehicle can show information, such as a map, without blocking the driver's view. A store display window can show not only products but also information about the products.
Three-dimensional (3D) transparent displays can enable another wide range of applications. Multi-dimensional scientific data can be visualized in 3D. Doctors can perform virtual surgery with greater precision. Engineers can create computer-aided design models in an actual 3D workspace. Oil and gas explorers can see exactly where to aim the drills. And audience members no longer have to wear special eyewear when watching a 3D movie in the theater.
A number of transparent display technologies exist, but none have gained a widespread usage. Eliminating the backlight of a liquid crystal display (LCD) increases its transparency, but only up to a transmittance of about 15%. An organic light-emitting diode (OLED) can also be made transparent, but OLED production remains costly and OLED transmittance is also limited (typically less than 40%). Electroluminescent displays have also been made transparent, but have so far been limited to single colors. Recently, fluorescent films have been combined with ultraviolet (UV) lights to make multi-colored displays that are transparent; however, intense UV sources are required due to the small emission cross sections of the fluorescent particles.
There has also been progress in 3D transparent displays, but such technologies have remained either in the lab or in specialized facilities. Technologies based on revolving 2D displays suffer from image flickering. Stacking several 2D displays yields a quasi-3D display with a limited viewing angle that cannot provide true 3D image depth. At least one prototype of a volumetric 3D laser display has also been demonstrated, but it was a miniature device, and its production is very difficult to scale. To date, none of these technologies has yielded a 3D display that is practical enough for consumer use.